One of the most important functions of clinical surgery is the resection and removal of undesirable tissues. During conventional resection surgery, the practitioner targets the undesirable tissue and using visual and tactile control, manually resects and removes that tissue. Resection implies that an incision is made in the skin to visually expose and gain access to the undesirable tissue. Not surprisingly, resection surgery usually results in considerable trauma to the patient. Until recently however, resection surgery was a generally preferred method of operating because the practitioner had confidence in the effectiveness of the procedure. This preference was primarily due to the fact that resection surgery led to, in most cases, complete removal of the undesirable tissue from the patient.
Minimally invasive surgery is an alternative surgical technique in which undesirable tissue is destroyed without necessitating resection and removal of the undesirable tissue. Minimally invasive surgical procedures can be performed using one of several known surgical techniques, the selection of which is usually determined by the type and extent of tissue to be destroyed and the location of the tissue. For example, prostate carcinoma is a common type of cancer which may be treated by using a percutaneous cryosurgical technique (a hypothermia application) in which the destruction of the tumour is accomplished by freezing.
In modern cryosurgical procedures, at least one cryoprobe having the general appearance and size of a conventional knitting needle is inserted into an undesirable tissue which is to be destroyed. The cryoprobe is provided with cooling sites typically located at the tip of the probe and cryobalation is performed by employing one of a variety of possible cooling means. Examples of such cooling means include: boiling of refrigerants; cooling of refrigerants; Joule-Thomson effects, etc. During the cryosurgical procedure, only a few small punctures are made through the skin of the patient where the cryoprobes are inserted. As is apparent from the foregoing discussion, a main objective of minimally invasive surgery such as cryosurgery is to minimize surgical trauma.
Other known surgical procedures which may be performed in a minimally invasive manner include hyperthermia, biopsy, alcohol ablation, and radiation seed implantation, photodynamic therapy and brachytherapy.
Minimally invasive surgical procedures have been shown to be effective for percutaneous contrast media injection and aspiration biopsy. Typical uses of this type of procedure include: ultrasonic Percutaneous Transhepatic Cholangiography (ultrasonic PTC) for suspected carcinoma of the bile ducts; ultrasonic Percutaneous Pancreatic Ductography (ultrasonic PPD) for suspected carcinoma of the pancreas; and ultrasonic Percutaneous Transhepatic Portography (ultrasonic PTP) for obstructing lesions of the portal vein. Other types of ultrasonographic aspiration biopsy of small intra-abdominal masses are well known and their uses have been extended to biopsy of the thyroid and breast.
One of the primary disadvantages of performing these types of procedures is that the practitioner is required to accurately guess the depth of the needle placement in the patient's body. Typically, the practitioner knows when the target tissue has been reached by the passage of a body fluid such as bile, pancreatic fluid or blood through the needle. However, the depth of penetration through the tissue is not known nor is the position and size of the suspected lesion. As will be apparent, it is important that the tissue which is the focus of the biopsy is carefully located such that the needle does not puncture other non-target organs such as the gallbladder, aorta or spleen. Unfortunately, in many situations, the visual quality of two-dimensional ultrasonography does not represent these vital structures clearly enough, especially when they are positioned behind the target tissue.
Guidance during minimally invasive procedures, and in particular, percutaneous procedures, refers to the ability to assist the practitioner during planning of the insertion points, target locations, and instrument trajectory.
Using conventional minimally invasive surgical techniques and instrumentation, imaging and guidance of instruments such as needles, probes and the like is very limited. Accordingly, the effective use of such instruments for these types of procedures requires an unusually high degree of practitioner skill. Two-dimensional imaging of the tissue is limited by virtue of the fact that only a single plane is in view at any one time and the plane of the view may be at the wrong orientation to properly image the procedure. Further, the required orientation of the two-dimensional image to guide instruments from an insertion point to a destination point may be impossible to achieve. This problem typically results from the inability to place the ultrasonographic transducer at the proper location due to factors such as patient position or bodily obstructions such as bone.
One of the most serious drawbacks of conventional techniques and instrumentation is the limited success rate and complications which can occur due to lack of practitioner skill and the significant level of guess work which typically accompanies such procedures. This can be attributed primarily to the lack of adequate imaging and instrument guidance indicated above. By way of example, in the past, when using procedures such as hypothermia, hyperthermia, and alcohol ablation, the practitioner has had to estimate the placement of the instruments and make an educated guess as to when to terminate treatment of the tissue. The educated guess approach when determining medical instrument placement, verification of placement and subsequently when to terminate treatment, primarily arises due to the inability to properly image and guide instrument placement in the tissue. The consequences of such guess work can be detrimental to the patient's health. For example, in the case of the cryosurgical prostatectomy procedure, the prostate is situated in close proximity to the rectal sphincter muscle, colon, urethra and bladder. Over freezing of the tumour into these regions may cause irreversible damage to these proximal organs, resulting in, for example, incontinence and impotence.
The above described disadvantages of minimally invasive surgical procedures were severe enough to make their use questionable for many years. However, recent improvement in two-dimensional and three-dimensional ultrasonography technology has resulted in improved resolution of the target image so that the extent of the affected tissue and efficacy of the treatment is more easily seen.
While the use of ultrasonography imaging has permitted visualization during a percutaneous medical procedure, the practitioner still experiences difficulties inserting and guiding medical instruments percutaneously to a selected target tissue. It is typically very difficult to maintain a constant trajectory to a target tissue and accordingly, during insertion, medical instrument often drift off course.
DE A 4010573 discloses a needle guide for carrying out ultrasound with an ultrasound probe. The needle guide comprises a flat plate of uniform thickness which has cylindrical openings provided in a grid pattern. The openings are provided for the guidance of puncture needles and therefore have a diameter which corresponds to the diameter of the puncture needles. The openings are conical in shape at the end which receives the puncture needle. The needle guide also has a mounting portion provided to receive an ultrasound probe. However, this needle guide assembly is deficient in that it does not permit precise control and positioning of a medical instrument.
Accordingly, there has been a long standing need for an apparatus to assist in guiding medical instruments percutaneously to a target tissue which overcomes at least one of the above-described disadvantages of conventional minimally invasive surgical procedures.